recently took my xjs over to the uk (i live in jersey ci/uk speed limit 40 mph) to visit my mum.I need to tell you wot iv changed so far ;most of the hoses,water pump,had the rad re-cored,new fan clutch,thermostats and changed the thermostatic switch for the electric fan. The car ran fine for one hour until i got to the motorway. Got the speed upto 80 mhp and the temperature guage started rising (all the time the lights were on). From just above the Ni.... H to just below the N....iH. At which point i pulled over at the service station to let the car cool down. Tried this once more, same as above. At this service there was an AA man and he put his laser gun on the hoses and it read a temperature of 90 degrees. Let the car cool right down again and proceeded on way way at about 50 mph for the next 150 miles. 5 caravans and a 2cv6 citroen overtook me!!!!At that part exchange for a new car was on my mind. Having got to my destination for the following week the car behaved perfectly, not going above 40 mph. Last chance saloon one the way back on the motorway the car was behaving good up to 70mph Ni....H got stopped in traffic started raining ans thought this would be good to keep the engine cool, at which point i turned the lights on and noticed the temperature rising instantly. N...i.H When the rain stopped 15 minutes later when the rain stopped the temperature instantly dropped to just above normal. At this point i started to experiment and took the car up to 100mph for the next 200 miles no problems.I think the temperature gage is a little out but as for the lights am guessing with it being a xjs their will be numerous reasons can any one please help. ps when its runing well theirs nothing id rather driv

 

Almost certainly you have a poor ground/earth at the instrument cluster. On my '88 it was the tachometer that went crazy with the headlights on :-)

Remove the cluster (we can provide details...it's not hard to do) and add a redundant ground wire from the metal bar (you'll see it at the back of the cluster) to a known-good ground point behind the dashboard.

Additionally, *gently* clean *all* the copper contact points on the printed circuit board.

Another thing that can cause up-n-down temp guage readings is air in the cooling system. Was the system properly bled after the hoses and water pump were replaced?

Cheers
DD

 

thanks Doug, ye bled the system .is the instrument cluster beined the ski slope or the cloks

 

The instrument cluster is the assembly containing the speedo, tach, temp gauge etc.

Cheers
DD

 

well iv taken the instrument panel out i can see the metal bar do i understand correctly ,i just get a new wire add it to the 2 that are already their and fix it to any part of the car that creates a good earth? sorry for my layman's terms of understanding.many thanks, pete